Low-water alarm



F 15, 1927- H. B. THURSTON LOW WATER ALARM Filed Feb. :5, 1926 gwuzwtoz mine; 5i

V. 253mm Patented Feb. 15, 1927.

UNITED STATES HERMAN B. rnuns'ron, or CLEVELAND HEIGHTS, OHIO.

LOW-WATER ALARM.

Application filed February This invention relates to a low vater alarm for steam boilers, and particularly for locomotive boilers. The essential object of the invention is to provide a low water alarm which will operate with certainty when the water in the boiler has descended to the minimum low safe level, but will not operate prematurely, notwithstanding the varying conditions within the boiler, which are extreme in arunning locomotive.

The invention is in the nature of an addition to a housing secured to the crown sheet and extending into the water space, a temperature responsive element within the housing and means controlled thereby and leading to the exterior for actuating the alarm. Such temperature responsive element may be a fusible plug normally closing a steam conduit leading from the boiler space to the exterior, and there may be a heat conveyin plug extending from the fire box to the region adjacent the fusible plug. Normally the water surrounding the temperature responsive element absorbs sutlicient heat so that such element will not operate to give the alarm, but when the water drops to a dangerously low level, the heat from the region of the temperature responsive element ceases to dissipate, resulting in the fusing of the plug or the operation of such element and the consequent actuation of the external signal.

In operating one form of such apparatus as described, I found that while it operated perfectly under various conditions,still in some instances it did not cause the alarm to be given at the desired water level, and in experimenting to overcome the detect 1 found that by placing a hood about the apparatus within the boilersuch hood having a roof portionsecured to the structure some distance above the temperature responsive element and having a depending wall out of connection with the structure in the region adjacent the temperature responsive ele ment-I could cure the ditliculty and cause the alarm to operate with uniform satisfaction.

The exact condition of water and steam within a boiler is unknown, but there is a theory that steam is condensed by the comparatively cold roof sheet, causing particles of water to descend through the steam, and thus that portion of the alarm control apparatus which is supposed to be in live steam,

3, 1926. Serial No. 85,654.

when the water reaches a certain low level may as a matter of fact be enveloped in a water precipitation, which may be likened to a rain storm, with a result that the heat about the fusible plug is conducted away so that it does not fuse as soonas expected. It has also been suggested that the heretofore undue cooling etl'ect of low water alarms in case of low water may be produced by the flying particles of water which burst from thesurface level of the water due to the rapid generation and escape of steam from the water in the region around the alarm, particularly when water level is nearing the top of the crown sheet.

Whether or not either ofthe above noted theories is correct, my tests in actual locomotive boilers have demonstrated that the hood described accomplishes the desired result. Such hood constitutes the subject matter of the present invention. It is shown in the drawings hereof in a preferred form and is hereafter more fully described, and its essential characteristics are summarized in the claims.

In the drawings, Fig. 1 is a vertical section through a boiler of the locomotive type alon the axis of my improved low water alarm; Fig. .2 is a horizontal cross SGCtlOIlsubstantially on the line 22 on Fig. 1 looking upwardly; Fig. 3 is a horizontal cross section through the structure at the lower end of the fusible plug; Fig. 4 is an internal perspective on an enlarged scale of either half of the hood detached.

While my protecting hood is adapted in principle for combination with various specific forms of low water alarm devices, it is shown herein as applied to the alarm device of application Serial No. 16,626 filed March 19, 1925, by Frank M. Roby and assigned to me. I will first describe such an alarm structure proper, in accordance with the description of that application. Reference should be had to that application for. further description and for claims on such structure.

Referring to Fig. l in detail and indicating the various parts by numerals, 1 is a section of the roof sheet of the boiler and 2 is a corresponding section of the crown sheet. The relative distance between these portions of the boiler is exaggerated by breaking away the alarm device and an adjacent stay bolt 3 as shown and bringing the sheets together for better illustrating the invention. As shown, the alarm device proper comprises passages leading from the steam space to a fusible plug and then outward through the boiler wall to a whistle. The passage preferably begins in a cavity 5 of combination packing fixture 6 which is in efieet a steam dome and which is shown as threaded into the roof sheet at 7. Projecting within the cavity, I have shown a tube 8, the end of which may be suitably spaced apart from the cavity walls in order that a connection may be maintained between the steam space and the interior of the tube.

The lower end of the tube 8 is shown as threaded into a bell shaped sleeve 9 which in turn has a threaded engagement with an upper flanged portion 11 of a plug cage 12. Passages 13 beginning in an annular groove 14 in this flanged portion 11 preferably communicate with a chamber 15 located in the lower region of the cage. The lower portion of this chamber may be closed by a heat conducting or fire box plug 17 threaded into'the cage'at 1S and extending downwardly through the crown sheet and preferably into the fire box as shown. This plug is shown as arranged to be easily removed by reason of the enlargement 20 at its lower end and for this reason the enlargement is preferably provided with angular faces.

Closing the passageway above referred to and extending into the chamber 15, I have shown a removable plug 22 having an angular head, a normally closed longitudinal opening 23 and transverse openings 2 1. The upper portion of the longitudinal opening in the plug may be filled with an easily fusible material such as pure tin or tin alloy as indicated at 25, and it will be noted that the cage is so built that direct heat conductivity is had to the walls of the plug' from the head 20, along the conducting member thence by way of th threads 18 to the portion of the cage.

To maintain the temperature of the cage surrounding the fusible plug low enough so that the plug will remain sol'd while there is a safe level of water over the crown sheet, I have cut the cage away as shown at 27 leaving simply enough material at this point to provide the desired strength and further to provide walls for the longitudinal passages 13.

The cage 12 has a flange 30 secured to the upper end of a casing 82, the lower end of which is preferably threaded into the crown sheet as at 35. The upper. portion of the jacket thus provided should be made as light as possible consistent with the required strength and corrosion resistance so that when the water level is below the zone of the flange 30, the cooling effect of the water on the cage will be reduced to a minimum. The fire box plug 20 is out of contemperature of the plug will be kept below tact with the casing 32, insuring a more efficient transfer of the heat from the the box to the above mentioned portion 18.

In the operation of the structure so far described it will'be apparent that so long 7 as the water over the crown sheet is of a depth sufficient to cover the cut away region 27 even periodically, (as when the water yin the boiler is in a surging condition), the

the melting point by reason of the slight amount of material between the cutaway portion 2'? and the fusible plug. That is to say, there will be enough heat drawn from the cage into the water to insure the plug remaining in a solid state.

l' owever, as soon as the water drops below the cut away portion 27 and stands about the water jacket 32, this heat absorbing effect of the water will be immediately -1 crably brazed and threaded into the top of the cage and which may extend through packing -10, a gland ll and apacking nut 12 to a whistle 4:3.

The hood, which constitutes the feature of this invention, is shown as made by two identical trough-like shells 50, each having a semi-annular end portion 51, and the two clamped together to make a substantially cylindrical jacket with a protecting roof. When so clamped, the roof has an annular groove 52 which embraces an external annular flange 10 at the top of the sleeve 9 whereby the hood is supported and cannot shift up or down. The hood wall 50 stands some distance outside of the alarm structure 1 proper and is out of contact with it. The roof 51 is secured directly to such wall for the most of the distance, but at two diametrically opposite points, there are vents .33 through the wall, and above each vent a 1 portion of the roof 51 extends beyond the vent in the form of a canopy 54: which has a downward skirt portion 55 the ends of which join the wall 50, as shown in lfig.

If the hood is made in the two parts illustrated, each part has along one edge of the wall and along half the roof a rabbet 56 formed by an outwardly offset portion 57 in which the opposite edge 58 of the other member seats, and beyond these edges are ears 59 for the reception of screw bolts for holding the two halves together. I have found it convenient to thread the ears on one section and leave the openings plain in the cars on the other section and to fasten the two parts together by bolts, the shanks of which pass through the smooth ears and are threaded in the threaded holes Such bolts are illustrated at in Fig. 2; they are preferably provided with screw driver slots for enabling them to be conveniently turned into position.

As my hood is attached at a point above the region of the fusible element 25, it willv in no way absorb the heat needed to cause the alarm to function. Moreover, as it does not receive any heat conducted up through the fire box plug 17 the walls of the hood will not be subjected to any greater scale deposit than other parts of the boiler equally removed from the crown sheet.

1 Due to the use of the two large covered vents near the top of the hood, the steam bubbles rising up near the alarm proper can easily escape, and it is believed that this movement, together with the natural circulation of water through the hood by reason of the vent openings,v assist in keeping the exterior of the alarm device proper, as well as the interior of the hood, free from scale or other deposits. The location of the vents prevents steam pockets in the region of the temperature responsive element which might interfere with the water absorbing heat when the water is at a general level above such region. The hood also acts as a protector of the alarm proper from damage due to its being struck by wash out pipes and the like when the boiler is being cleaned.

I have found that with such a hood as described the fusible plug acts as expected, according to the location of the plane dividing the water and steam, and accordingly the alarm acts with certainty and immediately whenever the water drops to a dangerous level.

Having thus described my invention, I claim:

1. In a low water alarm, the combination with a boiler and alarm proper, of a shield surrounding such alarm proper and supported by it but out of contact with it except above the region of the temperature responsive element and open to the normal water space of the boiler.

2. In a device of the character described, the combination with the boiler and the low water alarm proper within it, of a hood of inverted cup form attached to the low water alarm proper above the temperature responsive element and having a depending portion outside of and spaced from the casing surrounding such temperature responsive element and open to the normal water space of the boiler.

3. In a low water alarm, the combination with a casing within the boiler, a temperature responsive element therein and an external alarm controlled thereby, of a hood about the device having an impervious roof and a wallsome'distance outside of the cars ing terminating above the crown sheet of the boiler. I V

4. In a low water alarm, the combination of a casing connected to the crown sheet of a boiler, a temperature responsive element therein so located that it may be either in the water space or steam space, according to the rise and fall of the water, an external alarm controlled by such temperature responsive element, and a hood mounted on such device above the temperature responsive element, and having a protecting roof and a depending wall which is located beyond the casingv and is free therefrom at its lower end.

5. In a low water alarm, the combina tion with a boiler and alarm proper, of a hood surrounding such alarm proper and out of contact with it adjacent the region of the temperature responsive element, said hood having a covered vent near the top, the vent beinghigh enough to eliminaate the formation of any steam pockets which might prevent solid water surrounding the temperature responsive element, when water is at normal level. V

6; In a low water alarm, the combination with a boiler, of a housing therein carried by the crown sheet, a temperature responsive element within the housing, an externalalarm controlled by said element, a heat transmitting plug within the housing extending from the fire box to the region adjacent the temperature responsive element, and a hood supported by the housing above the temperature responsive element and hav-,

ing a skirt spaced some distance outside of said housing, there being a vent through the upper portion of such skirt.

7. In a low water alarm, the combination with a boiler, a housing therein carried by the crown sheet, a temperature responsive element within the housing, and an external alarm controlled by said element, of a hood supported above the temperature responsive element and having a skirt spaced some distance outside of said housing,-there being a vent through the upper portion of said skirt, and a canopy protecting the vent.

8. The combination with a low water alarm located above the crown sheet of a boiler, of a hood carried thereby and having a supporting roof and a depending skirt the interior of the hood being in. open communication with the normal water chamber of the boiler, said hood being made in sections clamped together about the alarm.

9. The combination with a low water alarm, having a temperature responsive ele-' ment and acasing surrounding the element and having an external shoulder above it, and a protecting hood engaging the upper and under surface of said shoulder and prevented thereby from shifting on the casing.

11. The combination with a low water alarm, having a temperature responsive element and a casing surrounding the element, and having an external shoulder above it and a protecting hood carried by said shoulder and comprising a separable member of inverted cup shape, the roof portion of which has a recess embracing said shoulder.

12. The combination with a low water alarm, having a temperature responsive element and a casing surrounding the element and a protecting hood comprising a two part member each part of which has a wall and a roof portion, said parts being provided with ears adapted to be bolted together, whereby the roof portion may be caused to embrace and engage the alarm and be suspended thereby.

13. The combination with a low water alarm, having a temperature responsive element and a casing surrounding the element and a protecting hood carried by the casing and comprising a two part member each part of which has a substantially semi-cylindrical wall and a semi-annular roof portion, said parts being provided with means whereby they may be secured together.

14. The combination with a low water alarm, 01": a hood therefor having a vent to allow circulation of a medium surrounding the alarm through the hood and protecting means lying above the vent to battle reentrance thereto.

15. A hood for a low water alarm comprising a roof portion, a skirt portion connected therewith, there being a vent ad]acent to the roof and protecting means arranged to bafiie the entrance fluid into the vent from a point outside the skirt, said means extending beyond the vent.

16. A hood for a low water alarm comprising a roof portion a skirt portion connected therewith, there being a vent through the skirt and a canopy extending beyond the vent. v

17. A hood for a low water alarm comprising a wall and a roof, there being a ventadjacent to the roof and the roof being continued beyond the vent and there depending lower than the vent.

18. A hood for a low water alarm comprising a wall and a root, there being a vent through the. wall adjacent to the roof and the roof being continued as a canopy beyond the vent and having a comparatively short depending skirt extending lower than the vent and at its edges engaging the wall proper.

19. A hood for a low water alarm comprising two parts each having a substantially semicircular skirt and a substantially semi-annular roof portion connected therewith at the arcuate edge, there being a vent through the skirt adjacent to the roof, and a canopy beyond the vent and there having a comparatively short depending skirt.

20. A hood for a low water alarm comprising two parts each having a substantially semi-circular skirt and a substantially semi-annular root portion connected therewith at the arcuate edge, the inner pcriplr cry of the annular root being provided with a substantially semi-circular groove.

QLA hood for a low water alarm comprising two parts each having a substantialy semi-circular skirt and a substantially semi-annular root portion connected therewith at the arcuate edge, one edge of each member being formed with a rabbet and the member being provided with ears adjacent opposite edges, whereby the parts may be bolted together.

In testimony whereof, I hereunto atlix my signature.

HERMAN B. THURSTON. 

